Field of the Invention
Embodiments of the present invention generally relate to highly sensitive magnetometers, and, in particular, to a system and method for making magnetic measurements by modulated excitation of atoms. More particularly, the invention relates to atomic magnetometers that rely on polarizing alkali metal vapor, and probing the state of magnetization of the polarized metal atoms.
Description of Related Art
Atomic magnetometers are based on detection of Larmor spin precession of optically pumped atoms. A spin-exchange relaxation-free (“SERF”) magnetometer achieves very high magnetic field sensitivity by monitoring a high density vapor of alkali metal atoms precessing in a near-zero magnetic field. In a magnetometer and/or a gyroscope based on that operating principle, it is necessary to measure the precession (i.e., rotation) of the atomic spin state due to the magnetic field with very high sensitivity. One of the most sensitive methods for measuring the Larmor spin precession is via the optical rotation of linearly polarized light propagating through the polarized alkali metal vapor. The highest polarization rotation sensitivity is achieved using two orthogonal polarizers, which are configured to extinguish the light, with the magnetometer cell and a polarization modulator between them. Magnetometers that use a polarization modulation technique use various types of polarization modulator subsystems such as a photoelastic modulator (“PEM”) or an electro-optic modulator (“EOM”). The use of a separate polarization modulator adds to the size and complexity of the sensor and can introduce noise and drift. Operation of some atomic magnetometers of the related art is described in U.S. Pat. No. 7,145,333, the entire content of which is hereby incorporated by reference in its entirety.
Therefore, a need exists to provide a miniature, highly sensitive atomic magnetometer having a high level of atomic spin coherence. The atomic magnetometers should have relatively low cost and low measurement drift at low frequency compared to the known art.